Modular Solar Power for Low-Cost, Responsive Missions

Abstract

The need for modularity in spacecraft solar arrays has become evident by the soaring non-recurring costs of custom solar arrays, which often exceed the actual costs of implementing the array. These expenses are driven largely by the requirements of industry standard specifications that demand extensive ground testing and qualification for new designs. Despite this stringent vetting, solar arrays remain the largest single source of on-orbit spacecraft failures. 1 The use of standard qualified modules will reduce or eliminate the bulk of the non-recurring expense associated with solar arrays while simultaneously increasing reliability since arrays can be identical to configurations that have previously been proven and flown. One area of rapid advancement in the field of solar arrays is with the photovoltaic device. Inverted Metamorphic Multijunction (IMM) cells offer increased performance with efficiencies expected to approach 40%. The inverted growth method yields a thin and flexible cell, allowing novel deployment concepts producing unprecedented specific power figures. However, the thinner cell is also fragile; industry standard laydown methods are not applicable and novel integration methods must be conceived. The IMM cell integration approach developed by Vanguard Space Technologies utilizes a modular, laminated assembly approach to achieve a robust solar array blanket that takes full advantage of the unique features of the IMM cell. The blanket is thin and flexible with high specific power, while maintaining a high degree of radiation protection. Materials used are standard in the industry and CTE matched to the photovoltaic cell. Vanguard has applied the modularity concept to the integrated IMM blanket. This occurs on two levels: first, submodules of 4- or 5-cells are assembled and interconnected. These can be laid down in any configuration as determined by the array requirements. A second level of modularity occurs when these sub-modules are applied to substrates that are modular themselves, such as the rigid panel modular array already developed by Vanguard. Finally, coverglass replacement technologies have been investigated as alternatives to industry-standard coverglass in order to take advantage of streamlined single-step manufacturing processes. Existing coverglass is typically matched one-for-one to each cell and requires a significant amount of labor to apply. Alternative covershield materials not only minimize labor costs but are also more conducive to a flexible solar array blanket which takes full advantage of the flexible nature of the IMM cell, allowing rolled solar arrays with high specific volume.